1. Field of the Invention
The present invention relates to an image capture apparatus, a method of controlling an image capture apparatus, and an electronic device. The present invention relates in particular to an image capture apparatus capable of shooting images (high dynamic range shooting) for creating a high dynamic range image, and to a method of controlling such an image capture apparatus, and an electronic device comprising or connected to such an image capture apparatus.
2. Description of the Related Art
High dynamic range (HDR) compositing is known in which multiple images captured with different exposure amounts (typically, standard exposure, under-exposure, and over-exposure) are composited to expand the dynamic range of an image. By compositing the standard exposure portions in the images, blown-out highlights and blocked-up shadows can be suppressed, and an image having a favorable tonal gradation from the dark portion to the bright portion can be obtained.
The dynamic range that can be realized by HDR compositing depends on the exposure conditions of the multiple images. For example, regarding a scene that has a wide dynamic range including a blue sky on a clear day as well as shadows of buildings and the like, an image in which the dynamic range of the scene is sufficiently reproduced cannot be obtained unless images are shot with an increased difference between the exposure amount in under-exposure and the exposure amount in over-exposure. On the other hand, with a scene on a cloudy day outside, the difference between the exposure amount in under-exposure and the exposure amount in over-exposure does not need to be significantly increased. Rather, when the exposure amount is set too high, there are cases where picture quality degradation such as S/N deterioration occurs since areas that are only slightly blown-out in standard exposure are compensated for more than necessary with under-exposure image signals that are not blown-out (quite dark), for example.
Thus, it is desirable that the difference between the exposure amount in under-exposure and the exposure amount in over-exposure (exposure range) are determined according to the scene dynamic range. Conventionally, there is a method in which a user manually selects this difference in exposure amounts out of ±1 EV, ±2 EV, and ±3 EV during shooting for HDR compositing, and also a method in which the difference in exposure amounts is automatically determined and set by the camera. For the latter method, it is common to use a method of determining the difference in exposure amounts based on scene dynamic range information acquired with an AE sensor having a wide metering field.
However, with light and compact camera systems such as so-called compact cameras and cameras built into portable devices and the like, it is necessary to acquire scene dynamic range information with another method since it is not necessarily the case that an AE sensor is built into those camera systems.
Japanese Patent Laid-Open No. 2010-183461 discloses that the dynamic range expansion amount is determined such that the amount of blown-out highlights is reduced, based on the amount of blown-out highlights in an image captured in standard exposure.
Additionally, in Japanese Patent No. 4554094, the degree of blocked-up shadows in the dark portions and the degree of blown-out highlights in the bright portions are analyzed based on a luminance histogram of an image captured in standard exposure. Also, a method is disclosed in which exposure conditions corresponding to the scene dynamic range are determined by repeating the shooting operation while changing the exposure conditions until the blocked-up shadows and blown-out highlights reach an allowable level.
With the method disclosed in Japanese Patent Laid-Open No. 2010-183461, the amount of blown-out highlights in the picture is an estimated value, and therefore, accuracy decreases in comparison to methods involving actual measurement. Also, although the method disclosed in Japanese Patent No. 4554094 is accurate since exposure conditions are determined based on images that are actually captured, there has been a problem in that the release time lag until the actual shooting is long since shooting and image analysis need to be performed multiple times in order to determine the exposure conditions.